Are You Smarter Than Slime Mold?

Tech Tidbits — June 2010

By
Dennis Simanaitis, Engineering editor

Apr 12, 2010

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I must confess that I'm no smarter than slime mold, at least when it comes to designing transportation networks. This revelation came to me after reading "Rules for Biologically Inspired Adaptive Network Design" in the January 22 issue of Science magazine, published by the American Association for the Advancement of Science.

Researchers collaborating in Japan and the U.K. studied Physarum polycephalum, a large, single-celled amoeboid organism that's known to forage for its food sources. Here's the cool part: In its foraging, this slime mold builds nutritional networks with a competence, fault tolerance and cost effectiveness comparable to those of human infrastructure design, in the researchers' case, comparable to the Tokyo rail system.

Modeling Tokyo On a Plate

In their experiments, the researchers put a lump of slime mold representing Tokyo on a 7-in. plate bounded by a simulated Pacific coastline and supplemented by food sources dotted at each of the region's major cities. For the first several hours, the slime's foraging strategy set out a contiguous cloud. Within 15 hours, it had colonized each of the food sources. Within 26 hours, it had concentrated links to the colonies as distinct paths, the totality having a significant resemblance to the Tokyo rail network.

Then researchers refined their study with illumination masks representing geographical constraints of the Tokyo region's mountains and inland lakes. The slime mold's response was a network that came even closer to the actual Tokyo rail system.

The Slime Versus Optimized Reality

Then came some theoretical fine-tuning of reality: The researchers applied a mathematical technique identifying the "minimal spanning tree," the shortest possible network connecting all the cities. They enhanced this theoretical network by connecting nearby cities that hitherto were linked only indirectly. This gave them an optimal theoretical network to compare with Tokyo's real railway system—and with the slime mold's version.

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The slime mold's network compared closely in transport efficiency with the optimized real one. In fact, using ratios of link length as a measure of cost, researchers concluded that the slime mold's version exhibited marginally lower expenditure overall. Alas, the slime wasn't as good as the theoretical model with fault tolerance, with what happened after a random failure. However, in terms of the tradeoff between cost and fault tolerance, it performed very well.

This, noted the researchers, was "without centralized control or explicit global information by a process of selective reinforcement of preferred routes and simultaneous removal of redundant connections." Pretty smart slime mold, I'd say.

Biomimics

Last, the researchers applied some biomimicry: They developed a mathematical algorithm that emulated behavior of the slime mold in adaptive network design. It starts with a randomly spaced lattice encompassing all the cities, er...food sources. The technique uses feedback loops comparing the thicknesses of each node's arteries with their flow. In subsequent iterations, tubes with higher flow rates get thicker; those with lower ones wither away.

How closely did their biomimicry mimic reality? "Judicious selection of specific parameter combinations yielded networks with remarkably similar topology and metrics to the Tokyo rail network," they said. What's more, they were able to fine-tune this biomimical technique to improve the system. Their work, they concluded, may have applications as well in wireless mesh networks, remote sensor arrays and other areas.

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Where to Park: In the House of Cars

If you happen to find yourself in Washington, D.C., between now and July 11, you might want to visit the National Building Museum's special exhibition, "House of Cars: Innovation and the Parking Garage." It's a showcase of the world's best architects and their efforts concerning where and how to park it.

Frank Lloyd Wright and Eero Saarinen each had thoughts on this. Today's innovations of "green garages" are also represented in the exhibition's sketches, engineering drawings and models. A lecture series is addressing urban planning and the future of transportation. A film series is also underway. Docent tours lasting 45 minutes start at 2 p.m. daily. The Museum is at 401 F Street NW. Museum hours are Monday through Saturday, 10 a.m. to 5 p.m.; Sunday, 11 a.m. to 5 p.m. Admission is free, though nearby parking may cost you. Check out .

LEDs Are Too Cool

An unintended consequence of fitting arrays of LEDs (light emitting diodes) to traffic lights is traceable to one of their advantages. These LEDs are particularly efficient—they consume 90 percent less energy than their traditional incandescent counterparts. Thus, they generate very little heat in their production of light.

It's so little, in fact, that traffic lights fitted with LEDs don't melt the ice and snow of inclement weather. Their housings become encrusted, to the detriment of visibility and function. The problem has been blamed for dozens of accidents and at least one death.

A proposed solution is installation of heating elements akin to those fitted to airport runway lights. Another one, albeit rather more labor intensive, is to have crews travel around and clean out the housings by hand. In St. Paul, Minnesota, for example, air compressors have been used to blow snow and ice out of malfunctioning traffic signals.

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I have yet to hear of anyone suggesting merely a return to the traditional incandescent bulbs.

Hardly a Bore's Tale (A Boar's Tail?)

Continuing the theme of unintended consequences, I can report that biofuel production in Germany and other European countries has led to a population explosion of Sus scrofa, the European wild boar. This, because wild boars absolutely love to (you'll excuse the expression) pig out on corn, rapeseed and other biofuel sources. Climate change is also being blamed, though I'm not certain I see the connection.

As reported in Der Speigel, attacks by boars have become commonplace. "Barely a week goes by in Germany without a news story about a human encounter with wild boars—joggers getting chased up trees, boars smashing their way into living rooms and tearing up the furniture, even whole hordes of the shaggy beasts rampaging through village streets." It's estimated that Germany's boar population is 2–2.5 million and increasing. Its human population is 82 million and decreasing. What can we learn from this? Discuss.

Lithium: In Trash Heaps and Geothermal Sources

I picked up an interesting lithium tidbit at the SAE 2010 Hybrid Vehicle Technologies Symposium. Given that Bolivia, Chile and China have the world's biggest supplies, the question arises, aren't we potentially swapping one cartel for another? No, say SAE experts. There's enough lithium to support something like 10 billion vehicles (itself, a sobering thought, as the world's total vehicle count is rather less than 1/10 of that today). In fact, some claim lithium won't even be an important aspect of battery recycling.

It's recycling their other materials that makes economic sense. Plus, there are environmental reasons for aggressive recycling.

Lithium is judged the Earth's 25th most common element, roughly akin to lead or nickel, with Canada, the U.S. and Australia cited as sources. It's contained in rock and clay formations as well as continental, oilfield and geothermal brines. In fact, according to a news item on the subject, a geothermal power plant southeast of Palm Springs, California, expects to extract a ton of lithium per month from waste water. If successful, the process could be used at similar facilities around the world.

I wrote a bit about geothermal power in "," August 2007, and also at roadandtrack.com. I've since learned that one of its tradeoffs is an extreme corrosiveness of geothermal ambience. In a sense, think of this lithium byproduct as a silver lining to that cloud of corrosion (most appropriate, as I've also learned that lithium is a soft, silver-white member of the alkali metal group).

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